The aim of this thesis is to determine the possible violation of the grammar norm smong students of fourth grade schools in Zadar County. More precisely, we want to determine the mastery of grammatical content among students at the end of the founrth grade. Also, in this paper we will exame how much difference there i sin breaking the normi in girls and boys. In the theoretical part of the work, we will define the Croatian standard language and what are its basic features. We will describe the normative manuals that are used for the use of the Croatian standard language and can help with a better understanding of it, we will explain the possible normative problems by word types and which grammatical errors most often occur when using the Croatian standard language. Furthermore, we will explain the grammatical norm as one of the norms that comprise the language standard of the Croatian language, we will explain what the teaching of the Croatian language includes according to the national curriculum for the subject of the Croatian language, what the students are expected to master accoring to the given outcomes, and finally give an overview contents of textbooks that are used in Croatian language classes. In the research part of the work, we will process the dana collected on a sample of 50 fourth-grade students. One village school, Braća Ribar Posedarje, which consists of the home school and five regional schools – Slivnica Gornja, Slivnica Donja, Ždrilo, Podgradina and Islam Latinski, and the city school Zadarski otoci participated in the research. The instrument of the research was a written test of grammatical content that the students processed through all four classes, and it consists of 10 tasks that include recognizing nouns, verbs and adverbs, determining the gender and number of nouns, distinguishing verbs of actions, states and events, pronouncing the past, prezent and future tenses in sentences, distinguishing possessive, descriptive and constrctive adjectives and forming adjectives and verbs from given nouns.